BEIRUT (Reuters) - One of Syria's strongest rebel factions, the conservative Islamist Ahrar al-Sham group, said on Wednesday it will not attend peace talks to be held in Kazakhstan on Jan. 23.

Several other leading rebel groups decided on Monday that they would be at the talks, which will be attended by the government of Syrian President Bashar al-Assad and are backed by Russia and Turkey.

Ahrar al-Sham said in a statement posted on social media that although it was not going, it would support the rebel groups that did plan to attend if they could achieve a beneficial result.

The talks come in the context of a ceasefire declared by Russia and Turkey at the end of last month that has reduced, but not ended, fighting between pro-government forces and rebels that began almost six years ago.

Ahrar al-Sham said its stance was in reaction to continued military activity by the Syrian army and Russian air strikes, and was aimed at preventing new divisions between those rebels who supported, and those who opposed, the talks.

Russia has waged an air campaign in support of Assad since October 2015 and the Syrian president is also backed on the battlefield by Iran and Shi'ite Muslim militias from Lebanon, Iraq and Afghanistan.

Turkey has been one of the biggest supporters of the mainly Sunni Muslim Syrian rebel groups but its main focus since last year has been on securing its border after a series of attacks within its frontiers by Islamic State and Kurdish militants.

Ahrar al-Sham has tried to maintain good relations with jihadist factions like former al Qaeda affiliate Jabhat Fateh al-Sham, but not Islamic State, as well as nationalist rebels supported by Turkey, Gulf monarchies and the United States.